The present invention relates to a valve drive mechanism having a rocker arm that is mounted on a cylinder head.
Small four-stroke engines such as are used in manually guided implements such as power chain saws, brush cutters, blowers, or the like require valve drives that have a simple construction and a small size. In order to save weight, the rocker arms, which are actuated by push rods, are embodied as components shaped from sheet metal, and are held on the cylinder head by support pins, whereby the pivot mounting of the rocker arm is embodied as a spherical mount. The valve stem of the poppet valve is engaged by one end of the rocker arm and is pressed firmly by the valve spring, as a result of which the rocker arm tends to pivot the mounting that is disposed between its ends. This is prevented by the push rod of the valve drive that engages at the other end of the rocker arm. The opening position of the poppet valve can therefore be varied with such a mounting by tightening or loosening the support pin, i.e. an adjustment nut that is threaded onto the support pin. In so doing, however, one must ensure that after adjustment of the valve play a securement of the pin or bolt head is effected in order to prevent an unintended altering of the valve play.
It is therefore an object of the present invention to provide a securement for the adjustment screw on the rocker arm of a valve drive that is easy to service has a straightforward configuration and does not adversely affect the overall height of the valve drive.